1. Field Of The Invention
The present invention generally relates to the fluidized conveyance of particulate solids. More particularly, the present invention relates to powdered coal distribution systems for fuel support of heat generating furnaces.
2. Description Of The Prior Art
In the utilization of coal as a fuel and raw material for activated carbon manufacture, moderate to large percentages of chunk coal are reduced to "dust" in handling and transit. For the purposes herein, dust may be defined as particles of approximately 40 mesh or less.
As a fuel, coal dust has excellent properties of high heat value and heat release rate. In practice, however, coal dust has proven to be a very difficult fuel to manage from the perspective of uniform combustion rate due to furnace feed and distribution complications.
In the case of activated carbon manufacture from coal where the volumetric rate of material processed is particularly large, proportionately large quantities of coal dust are generated. As to the manufacture of activated carbon product, coal dust is largely useless since the particles are too small to tolerate the selective oxidization process through a multihearth combustion furnace. Instead of carbonizing, hydrocarbons in the small particles are consumed by combustion leaving only fly ash. Such combustion within the product flow stream cannot be relied upon as a heat source to the process due to the erratic and uncontrolled nature thereof.
Accordingly, due to the large quantities of productively useless material having a high heat value, it would be particularly useful for activated carbon manufacturing facilities to utilize such material independently as fuel to fire the multihearth furnaces in which the parent material is provided stable, controlled heat for activation.
Unfortunately, however, multihearth carbon activation furnaces present a severe challenge to distributing coal dust due to the relatively complicated arrangement of requiring one or more fuel injection points on each of several, vertically spaced hearth levels.
The greatest difficulty in distributing coal dust is the tendency of the material to pack, within a fluidized flow stream, in "slugs" within the flow stream. As these slugs enter the combustion zone, combustion stability and uniformity of heat release suffer.
The following United States Patents represent prior art efforts at fluidizing a coal dust flow stream for furnace distribution: U.S. Pats. No. 2,053,340; 2,841,101; 2,960,324; 3,204,942; 3,267,891 and 3,306,238.
Such prior efforts have been less than satisfactory due to equipment complications or voluminous quantities of carrier medium (air) required for suspended flow.
It is, therefore, the object of the present invention to teach a method and apparatus for uniformly distributing coal dust in a fluidized flow stream as a fuel supply for heat generating furnaces.
It is another object of the present invention to teach a coal dust fuel distribution system wherein mechanical constituents having relatively few moving elements are isolated from the abrasive fuel mixture flow stream.
Another object of the present invention is to teach a low pressure, low carrier medium volume system for fluidized transport of coal dust.
Still another object of the present invention is to teach a process flow system for the manufacture of activated carbon wherein dust from raw material coal is utilized to heat the carbonization furnaces.